The goal of the proposed research project is to understand the developmental and molecular mechanisms that control morphogenesis during mammalian development. Our research is focused on the study of convergent extension, a process that mediates elongation of tissues and involves highly coordinated rearrangements/movements of cells. Numerous devastating congenital malformations result from aberrant coordination of cell movements, but the genetic basis of these diseases is in most cases unknown, which impedes their early diagnosis and prevention. Studies in amphibian and teleost vertebrates have revealed that non-canonical Wnt signaling regulates convergent extension. However, studies in mouse have indicated that convergent extension might be regulated by additional molecular mechanisms in mammals. A phenotype-based forward genetic screen identified chato, a mouse mutation causing embryonic lethality and convergent extension phenotypes. Our analysis of chato mutants confirmed that chato is required for the proper rearrangement of cells that lead to definitive endoderm convergent extension. chato encodes ZFP568, a novel Kruppel-Associated-Box (KRAB) Zinc finger protein. Analysis of chato embryos suggests that chato does not implement non-canonical Wnt signaling, but rather controls mouse elongation through an independent molecular mechanism. One of the goals of this proposal is to identify the molecular effectors and signaling pathways employed by chato to control convergent extension. We are also interested in understanding the developmental mechanisms utilized by chato: In addition to their convergent extension defects, chato mutants also display malformations in morphogenesis of extraembryonic tissues, which might indicate a role for these supporting tissues in promoting convergent extension. We will perform experiments to test this hypothesis. We have divided our research plan into three specific aims: In Specific Aim 1, we will determine whether extraembryonic tissues influence convergent extension of the embryo by analyzing the phenotype of tetraploid chimeras and genetic mosaic embryos. The study of chatwo mutants has provided genetic evidence supporting a role for TRIM28 as a transcriptional co-repressor of ZFP568. In Specific Aim 2, we determine the factors that influence formation of ZFP568-TRIM28 complexes and the mechanisms that mediate the specificity of this complex to the control of convergent extension. Finally, in Specific Aim 3, we seek to identify direct and indirect targets of ZFP568 and ZFP568-TRIM28 complexes and determine the ultimate ZFP568 effectors that control convergent extension. Overall, results from our experiments will increase our understanding of the molecules that control mammalian morphogenesis and provide insights about the molecular mechanisms utilized by KRAB Zinc finger proteins.